1. Field of the Invention
The present invention relates to an electrophotographic apparatus, an image forming method utilizing the electrophotographic process, and a process for fabricating a light receiving member for electrophotography used in the apparatus or in the forming method. More particularly, the present invention relates to an electrophotographic apparatus provided with a light receiving member for electrophotography having a surface of a non-monocrystal material comprising at least carbon, an image forming method using the photosensitive member, and a process for fabricating the light receiving member for electrophotography.
2. Related Background Art
In an image forming apparatus arranged to repeat a step of transferring a transferable toner image, formed on the surface of the light receiving member for electrophotography, to a transfer medium such as paper, the residual toner remaining on the surface of light receiving member after transfer is removed by a cleaning means.
The principal purpose of the cleaning process in the electrophotographic apparatus is to clean the surface of light receiving member by removing a residual image on the surface of light receiving member, i.e., by removing the toner (developer) remaining on the surface of light receiving member, for preparation for the next copying operation.
The known cleaning methods of the surface of light receiving member include the blade method, the fur brush method, the magnet brush method, and so on.
The blade method is a method for making a blade with elasticity like urethane rubber contact the surface of the light receiving member under rotation to remove the residual toner from the surface of light receiving member, which is used most popularly as a cleaning method because of its characteristics including feasibility of compact arrangement of the device for cleaning, relatively wide tolerance of setting conditions of device, and so on. A cleaning means of this type widely used heretofore is a cleaning blade of an elastic material such as rubber.
There are, however, some cases wherein use of only this cleaning blade is not always effective in removing deposits or the like such as fused toner, paper dust, rosin, or talc, fused and stuck to the surface of photosensitive member.
Proposed for compensating for incompleteness of the cleaning blade was a cleaning device arranged to remove the various deposit materials described above by urging a cleaning roller of an elastic material such as silicone rubber against the surface of photosensitive member and making the roller slide thereon.
There are cleaning devices proposed with use of either a magnetic cleaning roller composed of a sliding roller and a magnetic member, a cleaning roller to which a bias in the opposite polarity to the toner is applied, or a cleaning roller arranged so that the cleaning roller itself becomes the opposite polarity to the toner, and in such an arrangement that the cleaning roller is urged against the surface of photosensitive member and is made to slide thereon, thereby removing the various deposit materials described above.
The cleaning roller, as described above, is disposed in the cleaning device and a scraper is placed in contact therewith. The scraper is arranged to force the toner collected in the cleaning device (which will be referred to as collected toner) down into a collected toner reserving section with rotation of the cleaning roller, to coat the surface of cleaning roller with part of the collected toner, and to slidingly polish the surface of photosensitive member with the collected toner adhering to the coating surface, thereby slidingly removing the foreign materials described above and the powder such as the toner from the surface of photosensitive member.
A very effective means for achieving the good cleaning effect is to weaken adhesion of the residual toner adhering to the surface of light receiving member, in removing the residual toner from the surface of light receiving member by these cleaning methods.
In general, the toner on the surface of light receiving member adheres onto the surface of light receiving member by electrostatic force (Coulomb force and mirror reflection force) and van der Waals force. The adhesion by the electrostatic force can be relieved by eliminating electrical charge from the residual toner or the like, and the adhesion due to the van der Waals force can be relieved by a method of increasing the hardness of the surface of light receiving member or by a method for controlling the surface roughness or the like.
An example of the technology noting this point is the bulletin of Japanese Patent Application Laid-open No. 60-144746. This bulletin discloses the technology in which the surface of photosensitive member (=light receiving member) for electrophotography is made of an amorphous material containing silicon atoms and the surface is roughened so as to make the pitch and depth of unevenness of the surface of photosensitive member smaller than the average particle diameter of the developer to decrease the adhesion of toner, thereby enhancing cleanability.
This technology enabled to clean off the toner remaining on the surface of light receiving member down to some good level.
With demands for quicker copying speeds of copier or for further higher quality of copy image in recent years, however, it became necessary to control the surface condition of light receiving member more precisely.
Specifically, low-melting-point and small-particle-diameter toner materials are being used from the following reasons.
(1) The low-melting-point toner capable of being melted and fixed quicker than before was developed for fixing the toner quicker on the surface of transfer sheet to meet the demand for higher copy speed of copier. PA1 (2) Finer toner than before, i.e., the small-particle-diameter toner was developed for meeting the demand for higher quality of image. PA1 C=A.times.B1 PA1 C=E.times.B2 PA1 1.2.ltoreq.B1.ltoreq.6.0 PA1 0.01.ltoreq.B2.ltoreq.0.06 PA1 3.ltoreq.D/A.ltoreq.10
However, such low-melting-point and small-particle-diameter toner materials enable quicker copying and higher quality of image of copier on one hand, but they have a problem that they make cleaning harder on the other hand.
For example, the lower melting point raises the problem that fusion of toner to the surface of light receiving member becomes easier to occur than heretofore. Especially, in the case of an electrophotographic apparatus wherein the photoconductive layer is of a non-monocrystal material containing hydrogen atoms and/or halogen atoms in the matrix of silicon atoms, i.e., wherein an amorphous silicon (hereinafter referred to as a-Si) based light receiving member is used for the photoconductive layer, a drum heater is provided in the copier, whereby the surface temperature of the photosensitive member is controlled at about 40.degree. C. for preventing smearing of image (for example, Japanese Patent Application Laid-open No. 60-95551). Because of this, the surface temperature of light receiving member might increase to cause the residual toner to be fused to the surface of light receiving member in the image forming step, for example, at the start after long-term stop.
Even in the event of continuous operation, there are cases wherein the surface temperature increases as the surface of light receiving member is exposed to charge and exposure, so that the residual toner is also fused onto the surface of light receiving member.
With use of the small-particle-diameter toner, because the specific surface area thereof is larger than that of normal particle-diameter toner and because adhesion to the surface of light receiving member thus becomes greater, it makes harder to remove the residual toner from the surface of light receiving member than in the case of the normal particle-diameter toner. Accordingly, in the case of the low-melting-point plus small-particle-diameter toner, the possibility of occurrence of fusion to the surface of light receiving member becomes higher.
There thus occurred some cases wherein it became difficult to remove the residual toner or the fused toner well even with combined use of the cleaning blade and cleaning roller.
Repetition of copying processes in this state could result in notable occurrence of image defects such as "black dots", "white dots" or "black lines", "image unevenness" or the like, thus making it difficult to maintain the initial image quantity for a long term.